1) Technical Field of the Invention
The present invention relates to a semiconductor device and a manufacturing process thereof, and in particular to a transfer-mold type power semiconductor device and a manufacturing process thereof.
2) Description of Related Arts
A conventional transfer-mold type power semiconductor device, in general, includes a metal block having a mounting surface on which a power semiconductor chip such as an insulated gate bipolar transistor (IGBT) chip and a free wheel diode (FWD) chip is mounted via a solder layer. The power semiconductor chip includes a lower electrode (such as a collector electrode and a cathode electrode), an upper electrode (such as an emitter electrode, an anode electrode and a control (gate) electrode, if any). Also, the power semiconductor device includes a plurality of lead frames (terminals), at least one of which is electrically connected with the upper electrode of the Dower semiconductor chip via a thin wire of metal such as aluminum. Those components of the power semiconductor device are molded with resin covering the mounting surface of the metal block.
The power semiconductor device may include an insulating layer adhered on another surface opposite to the mounting surface of the metal block, and a metal thin layer formed on the insulating layer. In this case, the molded resin encompasses the metal block exposing the metal thin layer. The power semiconductor device is assembled with a heat sink (radiating fins, radiator) contacting with the metal thin layer. Another power semiconductor device may be mounted directly on the heat sink without the insulating layer. According to those conventional power semiconductor devices, heat generated in the power semiconductor chip is transmitted into the metal block and dissipated via the insulating layer or directly to the heat sink.
In the meantime, the heat dissipation feature from the power semiconductor device to the heat sink generally depends on the contacting area and the temperature difference between the metal block and the heat sink. Thus, in order to improve the heat dissipation feature, those skilled in the art may contemplate extension of the temperature difference and/or increase of the contacting area between the power semiconductor device and the heat sink.
However, if atmosphere temperature (e.g., ambient temperature of the heat sink) is constant, the temperature of the semiconductor chip has to be raised for extension of the temperature difference, thereby reducing the reliability of the semiconductor chip. Alternatively, increase of the contacting area prevents the power semiconductor device to be downsized. Also, even when the contacting area is extended, since the temperature inside the metal block decreases as being away from the power semiconductor chip, the heat dissipation feature cannot be improved as expected.